He asked about these new technologies and eventually became the
"test-pilot" for a bionic leg created by Todd Kuiken's team at
the Rehabilitation Institute of Chicago. The project was
partially funded by an $8 million grant from the U.S. Army.

The bionic leg uses electrodes and a microprocessor to read
Vawter’s intentions via muscle contractions in his thigh.

Normally, the brain sends electrical signals through the spinal
cord to instruct muscles to move. For a leg amputee, those
signals still occur, but there is no longer anywhere for that
signal to go. Because of this the nerves near the amputation site
tend to die off, leaving a dead circuit.

To avoid this, during the amputation, doctors rewired Vawter's
nerves so they could control muscle contractions in his thigh.
This kept the nerves alive.

Within a few months of the surgery, Vawter's nerves began
carrying electrical impulses to the muscles of his thigh. When
Vawter thought about curling his toes or moving his leg, his
thigh muscle contracted in distinct ways.

Vawter spent hours with his rewired thigh hooked up to
electrodes, while the team recorded the electrical signals
produced when he thought about making certain movements with his
leg. The team then used pattern recognition software to digitize
and catalog the movements.

The bionic leg was programmed to understand the signals and
respond with the appropriate movement or action.

"When the patient thinks about pushing his toes into the ground,
called plantar flexing or lifting, and pointing his foot up,
called dorsal flexing — essentially moving his ankle — instead of
causing muscle that is below his knee to contract, those nerve
signals have been redirected and his hamstring contracts," Levi
Hargrove, the lead researcher on the team, told Medscape.

They've been working on the prosthetic and the software that goes
with it for a long time, but now, it is nearly flawless — it
responds correctly 98% of the time.

It has been so successful that Vawter climbed to the top of the
103-story Willis Tower in Chicago last year,
according to The Chicago Tribune. Because the bionic leg is
still in development, Vawter does not get to use it every day.

Even when he does wear it, the bionic leg is not yet an
equivalent replacement for his real leg. Before his accident
Vawter could dunk a basketball. The prosthetic isn't good enough
to let him do that yet.

"It’s in between the leg I wear every day and prior to
amputation," Vawter
told Bloomberg News. "It’s a dramatic improvement over my
current prosthetic, but there is still a long way to go."

And the team is still going — they are making it lighter and
quieter, and improving battery life. Right now, the leg is good
for 5,000 steps or about 2.5 miles. The army wants it to be able
to perform twice that.

The technology could be on the market in three to five years,
according to Hargrove. But it only works with people who have had
their nerves attached to muscles in their thighs.